Abstract
Abstract. The coupled biophysical interactions between submerged aquatic vegetation (SAV), hydrodynamics (currents and waves), sediment dynamics, and nutrient cycling have long been of interest in estuarine environments. Recent observational studies have addressed feedbacks between SAV meadows and their role in modifying current velocity, sedimentation, and nutrient cycling. To represent these dynamic processes in a numerical model, the presence of SAV and its effect on hydrodynamics (currents and waves) and sediment dynamics was incorporated into the open-source Coupled Ocean–Atmosphere–Wave–Sediment Transport (COAWST) model. In this study, we extend the COAWST modeling framework to account for dynamic changes of SAV and associated epiphyte biomass. Modeled SAV biomass is represented as a function of temperature, light, and nutrient availability. The modeled SAV community exchanges nutrients, detritus, dissolved inorganic carbon, and dissolved oxygen with the water-column biogeochemistry model. The dynamic simulation of SAV biomass allows the plants to both respond to and cause changes in the water column and sediment bed properties, hydrodynamics, and sediment transport (i.e., a two-way feedback). We demonstrate the behavior of these modeled processes through application to an idealized domain and then apply the model to a eutrophic harbor where SAV dieback is a result of anthropogenic nitrate loading and eutrophication. These cases demonstrate an advance in the deterministic modeling of coupled biophysical processes and will further our understanding of future ecosystem change.
Highlights
Submerged aquatic vegetation (SAV), or seagrass, includes rooted vascular plants that inhabit sediments of estuaries and coastal waters, with a wide global distribution
The growth of SAV is dependent upon light availability at the leaf surface, which is a function of light attenuation in the water column and the biomass of epiphytic algae growing on SAV stems
We demonstrate the two-way biophysical coupling framework as follows: the SAV growth model and integration into Coupled Ocean–Atmosphere–Wave–Sediment Transport (COAWST) are discussed in Sect. 2; in Sect. 3, the model setup for the idealized domain and a realistic simulation of West Falmouth Harbor, Massachusetts, are described; in Sect. 4, we present the results from the two model configurations along with a discussion of limitations of the current modeling work; and in Sect. 5, we summarize our work and outline areas of future research
Summary
Submerged aquatic vegetation (SAV), or seagrass, includes rooted vascular plants that inhabit sediments of estuaries and coastal waters, with a wide global distribution. SAV involves important primary producers in shallow environments and provides a habitat for a number of aquatic organisms; it can slow water velocities and dampen wave energy to trap particulate material (Carr et al, 2010), as well as alter biogeochemical cycles through oxygenation of sediments (Larkum et al, 2006). One of the dominant factors of SAV loss is eutrophication through nutrient loading, exemplified by increased phytoplankton growth and epiphytic growth on vegetation. This results in a reduction of light availability (Burkholder et al, 2007), causing a loss of SAV habitat (Cabello-Pasini et al, 2003; Short and Neckles, 1999)
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